Viscous Kelvin-Helmholtz instabilities in highly ionised plasmas

Roediger, E.; Kraft, R. P.; Nulsen, P.; Churazov, E.; Forman, W.; Brüggen, M.; Kokotanekova, R.

Abstract

Transport coefficients in highly ionised plasmas like the intra-cluster medium (ICM) are still ill-constrained. They influence various processes, among them the mixing at shear flow interfaces due to the Kelvin-Helmholtz instability (KHI). The observed structure of potential mixing layers can be used to infer the transport coefficients, but the data interpretation requires a detailed knowledge of the long-term evolution of the KHI under different conditions. Here we present the first systematic numerical study of the effect of constant and temperature-dependent isotropic viscosity over the full range of possible values. We show that moderate viscosities slow down the growth of the KHI and reduce the height of the KHI rolls and their rolling-up. Viscosities above a critical value suppress the KHI. The effect can be quantified in terms of the Reynolds number Re = U{\lambda}/{\nu}, where U is the shear velocity, {\lambda} the perturbation length, and {\nu} the kinematic viscosity. We derive the critical Re for constant and temperature dependent, Spitzer-like viscosities, an empirical relation for the viscous KHI growth time as a function of Re and density contrast, and describe special behaviours for Spitzer-like viscosities and high density contrasts. Finally, we briefly discuss several astrophysical situations where the viscous KHI could play a role, i.e., sloshing cold fronts, gas stripping from galaxies, buoyant cavities, ICM turbulence, and high velocity clouds.

Citation

Roediger, E., Kraft, R. P., Nulsen, P., Churazov, E., Forman, W., Brüggen, M., & Kokotanekova, R. (2013). Viscous Kelvin-Helmholtz instabilities in highly ionised plasmas. Monthly notices of the Royal Astronomical Society, 436(2), 1721-1740. https://doi.org/10.1093/mnras/stt1691

• Journal Article Type: Article
• Acceptance Date: Sep 5, 2013
• Online Publication Date: Oct 3, 2013
• Publication Date: Dec 1, 2013
• Deposit Date: Mar 2, 2016
• Publicly Available Date: Mar 2, 2016
• Journal: Monthly notices of the Royal Astronomical Society
• Print ISSN: 0035-8711
• Electronic ISSN: 1365-2966
• Publisher: Oxford University Press
• Peer Reviewed: Peer Reviewed
• Volume: 436
• Issue: 2
• Pages: 1721-1740
• DOI: https://doi.org/10.1093/mnras/stt1691
• Keywords: Hydrodynamics, Instabilities, Plasmas, Methods : numerical, Galaxies : clusters : intracluster medium, X-rays : galaxies : clusters
• Public URL: https://hull-repository.worktribe.com/output/412003
• Publisher URL: http://mnras.oxfordjournals.org/content/436/2/1721
• Additional Information: This is a copy of an article published in Monthly notices of the Royal Astronomical Society, 2013, v.436 issue 2. This article has been accepted for publication in Monthly notices of the Royal Astronomical Society ©: 2013 The Authors. Published by Oxford University Press on behalf of the Royal Astronomical Society. All rights reserved.